This invention relates to watercraft and more particularly to watercraft with improved stability.
Various types of watercraft exist, each being suited for different types of activities. For example, a pontoon-type watercraft is designed for slower speeds and general recreational use and is typically powered by an outboard engine. In contrast, sport boats and personal watercraft are designed for higher speeds and superior handling and are powered typically by inboard jet drive systems, which consist of an inboard engine and a jet propulsion unit.
In a conventional sport boat, the engine is mounted above a jet propulsion unit. The intake for the jet propulsion unit is located beneath the watercraft and the exhaust, or jet port, is located at the rear of the watercraft.
There are several parameters that are engineered into a sport boat that may affect its performance. One of those parameters is the xe2x80x9cdrive line angle,xe2x80x9d which is the angle measured between the primary drive shaft (attached to the impeller) and the keel line of the watercraft.
Due to the physical characteristics of conventional jet drive systems in sport boats in the prior art, the drive line angle is typically about 4 degrees or greater. In a conventional watercraft, the positive angle of the drive line translates into an angle of thrust that is directed slightly upward toward the surface of the water, as illustrated in FIG. 2. The upward thrust angle has a tendency to push the bow of the watercraft out of the water. In other words, the positive drive line angle tends to lift the bow of the sport boat during operation.
U.S. Pat. No. 5,984,740 (the ""740 patent) describes and illustrates a personal watercraft 10, which incorporates a jet propulsion drive configured according to the teachings of the prior art. As illustrated in FIG. 3 of the ""740 patent, the impeller shaft 56 is angled upwardly from the keel line. The exact angle xcex1 of the impeller shaft 56, however, is not disclosed. The ""740 patent only discusses the advantages of a positive angle xcex1 for operation of the personal watercraft 10 described. (See. e.g. the ""740 patent at col. 5, lines 36-48.)
While those skilled in art may appreciate the benefits of a positive drive angle, a phenomenon known as xe2x80x9cporpoisingxe2x80x9d may be detected, at certain speeds, by occupants of certain boats. xe2x80x9cPorpoisingxe2x80x9d refers to a condition where the boat tends to move up and down in the water like the movement of a porpoise when it jumps out of the water. This can create an unpleasant ride for the occupants of the boat.
Conventionally, sport boats powered by jet propulsion units have all had positive drive line angles. In fact, conventional wisdom suggests that anything less than a positive drive line angle will so adversely affect vehicle performance that manufacturers of marine engines have specifically discouraged the incorporation of neutral (0xc2x0) or negative drive line angles in boats.
xe2x80x9cPorpoising,xe2x80x9d however, remains a problem with certain boat designs.
Accordingly, a need exists for a watercraft that utilizes a jet drive system with improved stability and reduced xe2x80x9cporpoisingxe2x80x9d to ensure that the occupants of the boat will experience a more comfortable and enjoyable ride.
It is, therefore, an object of the present invention to provide a watercraft, which provides the advantages of a jet propulsion system, with increased stability and reduced xe2x80x9cporpoising,xe2x80x9d by controlling the angle of thrust of the propulsion unit relative to the keel line.
One embodiment of the present invention provides a watercraft including a hull with a keel and a jet drive power source. The jet drive power source includes an engine, an engine output shaft, and a jet propulsion unit. The jet propulsion unit includes a water passage, a drive shaft, an impeller, and a jet port. The engine output shaft is operationally connected to the drive shaft. The jet drive power source is configured to produce power along a predetermined direction and form a drive line based upon the predetermined direction. The drive line bisects a plane of the keel at a predetermined, preferably negative, angle.
Other embodiments of the present invention will be discussed in or will be made apparent from the description that follows.